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See detailDisentangling soil from plant methanol exchanges in a maize field: a first step
Bachy, Aurélie ULg; Mozaffar, Ahsan ULg; Aubinet, Marc ULg et al

Poster (2016, June)

This poster presents the current research done in order to disentangle soil from plant methanol exchanges in a maize field. Methanol exchanges were calculated at ecosystem-scale (therefore including both ... [more ▼]

This poster presents the current research done in order to disentangle soil from plant methanol exchanges in a maize field. Methanol exchanges were calculated at ecosystem-scale (therefore including both components). It bases on the following observation: methanol exchanges on bare soil (measured when maize was at germination stage) were as important as when plants were fast growing (and thereby, when the highest methanol plant methanol emissions were expected), and this under similar weather conditions. The goal of this poster is thus to understand why emissions were similar at these two periods. First, it addresses the question of the actual contribution of maize plants in methanol exchanges, by comparing up-scaled methanol exchanges measured on maize at leaf-scale (Mozaffar A.) to those measured at ecosystem-scale. Then, it investigates methanol exchanges mechanisms in order to evaluate how did soil methanol emissions evolve along the maize growing season. At the end of this poster, the hypothesis of decreasing soil methanol emissions along the maize growing season is proposed. [less ▲]

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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

in Atmospheric Chemistry and Physics (2016), 16(8),

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale ... [more ▼]

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale and over a whole growing season. This has led to large uncertainties in cropland BVOC emission estimations. This paper seeks to fill this gap by presenting, for the first time, BVOC fluxes measured in a maize field at ecosystem scale (using the disjunct eddy covariance by mass scanning technique) over a whole growing season in Belgium. The maize field emitted mainly methanol, although exchanges were bi-directional. The second most exchanged compound was acetic acid, which was taken up mainly in the growing season. Bi-directional exchanges of acetaldehyde, acetone and other oxygenated VOCs also occurred, whereas the terpenes, benzene and toluene exchanges were small, albeit significant. Surprisingly, BVOC exchanges were of the same order of magnitude on bare soil and on well developed vegetation, suggesting that soil is a major BVOC reservoir in agricultural ecosystems. Quantitatively, the maize BVOC emissions observed were lower than those reported in other maize, crops and grasses studies. The standard emission factors (SEFs) estimated in this study (231 ± 19 µg m−2 h−1 for methanol, 8 ± 5 µg m−2 h−1 for isoprene and 4 ± 6 µg m−2 h−1 for monoterpenes) were also much lower than those currently used by models for C4 crops, particularly for terpenes. These results suggest that maize fields are small BVOC exchangers in north-western Europe, with a lower BVOC emission impact than that modelled for growing C4 crops in this part of the world. They also reveal the high variability in BVOC exchanges across world regions for maize and suggest that SEFs should be estimated for each region separately. [less ▲]

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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Conference (2016, April 18)

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the ... [more ▼]

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the interest of investigating BVOC exchanges on maize; then measurement techniques are briefly presented. The second half of the communication aims to present and discuss the main outputs of this measurement campaign (similar BVOC composition, lower exchange rate than other maize and cropland/grassland studies, significant importance of soil in ecosystem exchanges, strong differences between exchanges rates observed in this study and those used by up-scaling models). [less ▲]

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See detailInterpreting canopy development and physiology using a European phenology camera network at flux sites
Wingate, L.; Ogée, J.; Cremonese, E. et al

in Biogeosciences (2015), 12(10), 5995-6015

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and ... [more ▼]

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring `green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future. [less ▲]

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See detailNitrous oxide flux measurement with a closed chamber system : data treatment
Regaert, Donat ULg; Moureaux, Christine ULg; Heinesch, Bernard ULg et al

Poster (2015, January 30)

Nitrous oxide flux estimation from concentration measurements with a closed chamber system. Statistical data treatment to sort between relevant/irrelevant fluxes.

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See detailCarbon balance of a grazed pasture and its response to grazing management
Jerome, Elisabeth ULg; Gourlez de la Motte, Louis ULg; Beckers, Yves et al

Poster (2014, September 24)

The C balance of a grazed pasture situated in Condroz (Wallonia) and its dependence on climatic conditions and grazing management were investigated on the basis of eddy covariance measurements and ... [more ▼]

The C balance of a grazed pasture situated in Condroz (Wallonia) and its dependence on climatic conditions and grazing management were investigated on the basis of eddy covariance measurements and horizontal C flow estimates. In average on three years, NEE was +43±24 gCm-2yr-1 and NBP was +7±26 gCm-2yr-1, suggesting that that the site is C neutral. Management by the farmer (organic fertilization), but also climate conditions influencing management (feed supplements), were the main factors impacting the C balance inter-annual variability. At a daily and seasonal scale, grazing impact on CO2 fluxes did not appear explicitly, being blurred by flux response to climate drivers. It was highlighted by specific investigations. The indirect grazing impact (photosynthesizing biomass consumption, excretions, soil compaction) was deduced from an analysis of the flux to PPFD response evolution during grazing period; the direct impact (livestock respiration) was investigated through confinement experiments. Result showed that saturation GPP changes were negatively correlated to grazing intensity (product of the stocking rate and grazing duration). On the contrary, no significant change in TER was observed. The direct impact of grazing due to cattle respiration was estimated to 2.59±0.58 kgCLU-1day-1, i.e. 8% of the TER. [less ▲]

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See detailAre agricultural ecosystems important BVOC « exchangers »? Evidences from 2 measurement years on croplands at Lonzée Terrestrial Observatory (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Poster (2014, September 23)

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile ... [more ▼]

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile Organic Compounds) emission from terrestrial ecosystems. Indeed, those compounds which are mostly emitted by plants play a great role in the atmospheric chemistry, thereby influencing the Earth surface radiative budget and the tropospheric air quality. However, so far, very few is known about BVOC exchange by crops, implying that huge uncertainties remain about qualifying, quantifying and determining sources/sinks and driving mechanisms of BVOC exchanges between croplands ecosystems and the atmosphere. We present here the first long term BVOC fluxes measurement study conducted on maize (2012) and winter wheat (2013), respectively the second and first most important worldwide crops (FAOSTAT). BVOC exchange was measured using the disjunct by mass scanning eddy covariance technique (+ PTR-MS, Ionicon) at the Lonzée Terrestrial Observatory (ICOS site) in Belgium. Main results are: (i) crops emit mainly methanol; (ii) BVOC emission from studied crops is lower than in literature, suggesting that agricultural ecosystems are poor BVOC exchangers; (iii) soil is a significant BVOC source. [less ▲]

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See detailAre agricultural ecosystems important BVOC « exchangers »? Evidences from 2 measurement years on croplands at Lonzée (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Poster (2014, July 01)

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile ... [more ▼]

For the last decades, agricultural ecosystems have been a key biome for diverse socio-economical, environmental and climatic issues. And one of these climatic issues is just BVOC (Biogenic Volatile Organic Compounds) emission from terrestrial ecosystems. Indeed, those compounds which are mostly emitted by plants play a great role in the atmospheric chemistry, thereby influencing the Earth surface radiative budget and the tropospheric air quality. However, so far, very few is known about BVOC exchange by crops, implying that huge uncertainties remain about qualifying, quantifying and determining sources/sinks and driving mechanisms of BVOC exchanges between croplands ecosystems and the atmosphere. We present here the first long term BVOC fluxes measurement study conducted on maize (2012) and winter wheat (2013), respectively the second and first most important worldwide crops (FAOSTAT). BVOC exchange was measured using the disjunct by mass scanning eddy covariance technique (+ PTR-MS, Ionicon) at the Lonzée Terrestrial Observatory (ICOS site) in Belgium. Main results are: (i) crops emit mainly methanol; (ii) BVOC fluxes from studied crops is lower than in literature, suggesting that agricultural ecosystems are poor BVOC exchangers; (iii) soil is a significant BVOC source. [less ▲]

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See detailImpact of grazing on carbon dioxide exchanges in an intensively managed Belgian grassland
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

in Agriculture, Ecosystems & Environment (2014), 194

Given that the soil carbon (C) sequestration potential by grasslands can be used to partly mitigate the total greenhouse gas emissions of livestock production systems, a better understanding of the ... [more ▼]

Given that the soil carbon (C) sequestration potential by grasslands can be used to partly mitigate the total greenhouse gas emissions of livestock production systems, a better understanding of the effects of management practices, and especially grazing, on grassland carbon dioxide (CO2) exchanges has become a major concern. This study aimed at quantifying grazing impact on CO2 fluxes measured by eddy covariance by using innovative data analyses and experiments. For that, we distinguished direct and indirect grazing impact. Indirect impact results from biomass consumption, excretion deposits and soil compaction by cattle that modify CO2 exchanges. Direct impact results from livestock CO2 emissions through respiration that add to total ecosystem respiration. For the indirect impact, the variation during periods with fixed stocking rate of gross primary productivity at light saturation (GPPmax) and normalized dark respiration (Rd,10) was analyzed. On average, GPPmax decreased during grazing periods and increased during non-grazing periods which could be explained by aboveground biomass reduction and re-growth, respectively. In addition, GPPmax variations were negatively correlated to grazing intensity (defined as the product of the stocking rate and the grazing duration). On the contrary, no significant evolution of Rd,10 was found during both grazing and non-grazing periods, probably due to a combination of opposing effects of grazing on the total ecosystem respiration components. The direct impact was emphasized through four specific designed confinement experiments. Each experiment extended over three successive days. On the first and third day, there was no cattle on the plot, while, on the second day, cattle were confined in the main wind direction area of the eddy covariance set-up to increase the stocking rate (≈26livestockunitsha-1). The average livestock CO2 emissions during confinement, FCO2,livestock, were deduced from the differences between half-hourly measurements taken at 24h interval with or without cattle and under similar environmental conditions. They were estimated to be 2.59±0.58kgClivestockunit-1d-1 on average. This result was corroborated by independent estimates based on the C ingested by cattle during confinement. Using an annual average stocking of 2livestockunitsha-1, we found that livestock CO2 emissions represent only 8% of this grassland annual total ecosystem respiration. To our knowledge, this study is the first to quantify both direct and indirect livestock contribution to CO2 fluxes exchanged at the ecosystem scale using the eddy covariance technique. © 2014 Elsevier B.V. [less ▲]

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See detailEtablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage. Rapport de synthèse. Janvier 2012 – Décembre 2013.
Jerome, Elisabeth ULg; Dumortier, Pierre ULg; Beckers, Yves ULg et al

Report (2013)

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone ... [more ▼]

Dans l’optique d’une atténuation des émissions de Gaz à Effet de Serre (GES) des systèmes d’élevage, les écosystèmes prairiaux peuvent jouer un rôle important vu leur potentiel de séquestration de carbone (C) dans les sols. Une évaluation pertinente de la contribution des systèmes d’élevage herbivores aux émissions de GES nécessite de raisonner en termes de bilan, en considérant à la fois les sources de GES et leur compensation via la séquestration de carbone par les prairies. Le projet « Etablissement du bilan de carbone d’une exploitation agricole wallonne pratiquant le système allaitant : effets du climat et de la gestion du pâturage » a pour objectif d’établir un inventaire de la contribution nette des systèmes d’élevage en Wallonie aux flux de GES (CO2, N2O, CH4). A long terme, nous étudierons les possibilités de réduction de ces émissions nettes par des adaptations des modes de conduite des systèmes d’élevage en adéquation avec leurs objectifs économiques et sociaux. L’exploitation étudiée est une exploitation agricole du type « naisseur-éleveur ». L’élevage se compose de vaches allaitantes et des veaux non sevrés de l’année de race « Blanc Bleu Belge culard ». Le système d’alimentation se base essentiellement sur la prairie permanente durant la période estivale et les produits conservés de la prairie durant la période hivernale. Ce rapport constitue l’état d’avancement du projet au terme de la deuxième biennale. [less ▲]

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See detailNitrous oxide emissions using quantum cascade laser spectrometry over a production crop: preliminary results
SALERNO, Giovanni ULg; Aubinet, Marc ULg; Joly, Joly et al

Poster (2013, September 18)

Amongst the greenhouse gases, nitrous oxide is recognized as having the greatest greenhouse forcing potential and as being the third in terms of radiative forcing. Agriculture is known to be the major ... [more ▼]

Amongst the greenhouse gases, nitrous oxide is recognized as having the greatest greenhouse forcing potential and as being the third in terms of radiative forcing. Agriculture is known to be the major anthropic emitter. This work is part of the FERTECOL project and its objective is to measure the emissions of nitrous oxide by a production crop with an eddy covariance system. The measurements extent over the growth period, cover a large range of climatic conditions and capture peak events associated with fertilization. The measurements, started in April 2013, are carried at the Lonzée Terrestrial Observatory (50°33'5.83"N- 4°44'46.22"E). On this year, the crop is planted with winter wheat. A Quantum Cascade Laser Absorption Spectrometer (QCLAS, GSMA, France) is used to measure nitrous oxide as well as water vapor and carbon dioxide at a frequency of 5 hertz. The fluxes are computed using the Eddy Covariance technique adapting standards quality and corrections procedures set up for CO2 fluxes to N2O. Standard meteorological measurements are performed in parallel. The analysis will present response of the fluxes to environmental variables as well as to fertilization events during the season. [less ▲]

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See detailImpact of grazing on carbon dioxide flux exchanges in an intensively managed grassland
Jerome, Elisabeth ULg; Beckers, Yves ULg; Bodson, Bernard ULg et al

Poster (2013, September)

To date, there are few studies assessing the impact of specific management events, particularly grazing, on carbon (C) and carbon dioxide (CO2) fluxes in managed grasslands. Grazing effects are indeed ... [more ▼]

To date, there are few studies assessing the impact of specific management events, particularly grazing, on carbon (C) and carbon dioxide (CO2) fluxes in managed grasslands. Grazing effects are indeed difficult to discern. They vary with the stocking rate and the length of the grazing period. Moreover, they are often masked by environmental responses. The aim of the present study was to assess the impact of grazing on the CO2 fluxes of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne Terrestrial Observatory (DTO), located in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.). The site is a permanent grassland of ca. 4.2 ha subjected to intensive management. Grassland carbon budget at the system boundaries is calculated from Net Ecosystem Exchange of CO2 measured by eddy covariance by taking imports and exports of organic C and losses of carbon as methane into account. After 2 years of measurements, the site was close to equilibrium. If management practices (harvest, fertilization and imports as supplementary feedings) and climatic conditions had a significant impact on the C balance, the impact of grazing was uncertain, especially on CO2 fluxes. To do this analysis, we distinguished the long term and the short term impacts of grazing on CO2 fluxes. The long term effect results from the biomass consummation by the cattle and from the cattle effluents that modify assimilation and respiration fluxes. This could be quantified only by comparing fluxes before and after grazing periods. The short term impact is due to cattle respiration that is a part of total ecosystem respiration and should be measured in its presence in the field. For the long term effects of grazing on CO2 fluxes, we analyzed the temporal evolution of gross maximal photosynthetic capacity GPPmax and dark respiration normalized at 10°C (Rd,10). Those parameters were deduced from the response of daytime CO2 fluxes to radiation over 5-day windows. We calculated parameters variations between the beginning and the end of grazing and non-grazing periods (∆GPPmax, ∆Rd,10) and analyzed their dependence to stocking rate. We found a significant decreased of ∆GPPmax that allowed us to quantify the assimilation reduction due to grass consumption by cattle. Discrimination of this impact from flux response to climate was possible only after gathering and treating two years of measurements taken under various climatic conditions. At the opposite, no significant evolution of Rd,10 with the average stocking rate was found. The short term impacts were an increase of CO2 fluxes in presence of cattle. It could be distinguished and quantified only thanks to confinement experiments. Each experiment extended over two days: the first day, cattle was confined in the footprint of the eddy covariance set-up (1.76 ha, 27 LU ha-1) and the second day, it was removed from it. We compared filtered half-hourly data made at 24h intervals, in the presence or absence of cattle, considering that environmental conditions were equivalent (air temperature, wind speed, radiation and wind direction). Livestock contribution to CO2 fluxes was estimated to be 2.25 ± 0.68 kg C LU-1 d-1. [less ▲]

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See detailMesures des flux in situ de gaz à effet de serre (N2O, CO2, H2O …) avec la station ECoFlux (Eddy Covariance Flux
Joly, Lilian; Decarpenterie, Thomas; Dumelié, Nicolas et al

Conference given outside the academic context (2013)

La concentration atmosphérique en gaz à effet de serre, responsable du réchauffement du climat, ne cesse d'augmenter depuis le début de l'ère industrielle. Les hypothèses médianes du groupe international ... [more ▼]

La concentration atmosphérique en gaz à effet de serre, responsable du réchauffement du climat, ne cesse d'augmenter depuis le début de l'ère industrielle. Les hypothèses médianes du groupe international d'experts sur le changement climatique (IPCC) prédisent un doublement de la concentration en dioxyde de carbone (CO2) avant la fin de ce siècle. De plus, la concentration d'autres gaz à effet de serre au pouvoir radiatif supérieur à celui du CO2 augmente, comme par exemple le méthane (CH4) et le protoxyde d’azote (N2O). Le N2O présente un potentiel de réchauffement d’environ 310 fois plus élevé que celui du CO2 avec une durée de vie de 120 à 150 ans. Son augmentation actuelle de 0.3% par an de sa concentration est imputable à l’activité anthropique incluant des processus industriels via l’utilisation de solvants mais surtout aux activités agricoles pour environ 70% via des processus biologiques de nitrification et dénitrification se produisant dans les sols. Afin de mieux comprendre l’effet des pratiques agricoles sur les échanges gazeux entre les sols et l’atmosphère, il faut quantifier les flux réels en fonction des différents types de sols, de pratiques culturales, de climats et d’écosystèmes. La limite actuelle de mesure de ces flux (notamment pour le N2O) réside dans la mauvaise sensibilité et stabilité des instruments de mesure en conditions de terrain. Depuis peu le GSMA (Groupe de Spectroscopie Moléculaire et Atmosphérique) a mis au point une station nommée ECoFlux (Eddy Covariance Flux) utilisant un senseur innovant reposant sur la spectrométrie laser infrarouge. Il permet de déterminer simultanément les flux in situ de N2O, CO2 et H2O par la méthode de covariance. Après une présentation du principe de la station ECoFlux, nous exposerons les résultats de deux campagnes de mesure sur des sites « grandes cultures » de suivi de gaz à effet de serre appartenant au réseau ICOS (http://www.icos-infrastructure.eu/). Nous terminerons en développant les intérêts et les modalités du déploiement de cette station sur site viticole [less ▲]

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See detailLong term measurements of VOC exchanges above a maize field at Lonzée (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; SALERNO, Giovanni ULg et al

Poster (2013, June 10)

For the last decades, VOC had arisen scientifict interest due to their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Terrestrial ecosystems being ... [more ▼]

For the last decades, VOC had arisen scientifict interest due to their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Terrestrial ecosystems being the main VOC source, evaluation of current and future biogenic VOC emissions through VOC exchange modeling is thus necessary to better estimate future climate and assess future air pollution risks. BVOC exchanges depend on edaphic variables and are plant species specific. Therefore, their modeling and global budget evaluation requires a comprehensive understanding of production and exchange dynamics under a wide panel of climatic conditions and ecosystems, which necesserily implies BVOC exchange measurements under varied conditions. In that perspective, forest and non pastured grasslands have been largely studied for the last decade, but knowledge about BVOC fluxes from croplands remains still scarce. As a consequence, crop species-specific standard emissions that feed bottom-up BVOC emission models are still often assigned to a default value that is in addition kept constant for the entire growth season, although recent research has shown that plant phenology, acclimation and stress can drastically influence BVOC emissions. To help filling this knowledge gap, we run a project that aims to study VOC fluxes from two major croplands, maize (2nd most important culture worldwide) and winter wheat (1st most important culture worldwide), and a pastured grassland. We present here a specific study focussing on the VOC exchanges between a maize field and the atmosphere. VOC fluxes were measured at ecosystem-scale during the whole 2012 growing season using the eddy covariance by mass-scaning technique with a proton-transfer-reaction mass spectrometer. Together with VOC fluxes, we also recorded a wide set of ancillary data including CO2 fluxes, meteorological variables and biomass evolution. As far as we know, we are the first study dealing with BVOC measurements on maize at ecosystem scale and spanning all the phenological stages of the crop. Although first results show half-hourly bidirectionnal exchanges among all the preselected compounds, in average methanol is the greatest emitted VOC, followed by green leaf volatiles. Acetic acid and acetaldehyde are the greatest taken up VOC. Small isoprene and monoterpene fluxes are also observed. A diurnal pattern is found for all those VOC, with greater emission/uptake during the day, suggesting a flux dependence on environmental parameters. Influence of environmental controls, biomass evolution (including growth primary production) and phenology on fluxes is currently under investigation. Our research allows to quantify BVOC exchanges by a maize field throughout a whole growing season. Hence, obtained results will refine the understanding of the BVOC exchanges mechanisms by including both environmental and phenological parameters. Such results are expected to be very useful for BVOC modeling, especially for oxygenated compounds such as methanol. [less ▲]

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See detailTemporal variability of nitrous oxide fluxes from a fertilized grassland in Belgium: preliminary results from dynamic closed chambers.
Beekkerk van Ruth, Jöran ULg; Moureaux, Christine ULg; Degré, Aurore ULg et al

Poster (2013, April 09)

Presentation of preliminary results from N2O measurements over a grassland using dynamic closed chambers. See attached folders for more detail.

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See detailTEMPORAL VARIABILITY OF N2O FLUXES FROM A FERTILIZED GRASSLAND: PRELIMINARY RESULTS FROM DYNAMIC CLOSED CHAMBERS
Beekkerk van Ruth, Jöran ULg; Moureaux, Christine ULg; Degré, Aurore ULg et al

Poster (2013, April 09)

This work presents preliminary results of nitrous oxide (N2O) fluxes measured by dynamic closed chambers from a fertilized grassland grazed by the Belgian Blue breed of cattle. It is part of a project ... [more ▼]

This work presents preliminary results of nitrous oxide (N2O) fluxes measured by dynamic closed chambers from a fertilized grassland grazed by the Belgian Blue breed of cattle. It is part of a project funded by the public service of Wallonia (SPW-DGARNE), whose objectives are to make a carbon/CO2 balance of the grassland (Jérôme et al., 2013) and to quantify CH4 (Dumortier et al., 2013) and N2O fluxes. The site is located in Dorinne (Dorinne Terrestrial Observatory), Belgium (50° 18’ 44” N; 4° 58’ 07” E; 248 m al.). It is a permanent grassland of ca. 4.2 ha with a moderate slope of 1 to 2 %. Mineral fertilisation took place in March and May 2012. Two cylindrical chambers of 19,2 cm diameter and 11,5 cm height were placed inside a protected area around a micrometeorological station. An infrared gas analyser (Thermofischer 46i) was used in order to measure the N2O concentrations inside of the chambers, closed by automatically controlled lids and ventilated by a constant air flow of 1liter/min. These devices were completed by adjacent soil humidity and temperature sensors. The first measurement campaign took place during June and July 2012. The chambers were installed in the field and N2O fluxes were followed without manipulation. N2O fluxes were characterised by a background emission (between 2 and 10 ngN.m2s􀀀1) on which intense but time limited peaks (between 50 and 300 ngN.m2s􀀀1) superimposed. Peaks were found to be mainly linked to fertilisation and driven by precipitation. Background fluxes were found to correlate positively with soil temperature. Secondly, a manipulation experiment took place in November 2012: two different fertilizer treatments were applied to the chambers. Doses of respectively 100 and 200 kg N/ha of ammonium nitrate were sprayed in the chambers (equivalent to a 8mmprecipitation). N2O fluxes peaked shortly after fertiliser application (respectively 300 and 550 ngN.m2s􀀀1), as well as after a posterior rain event (respectively 800 and 1500 ngN.m2s􀀀1). The peak dynamics suggests a complex interaction between soil humidity and nitrogen availability, which is under study. Dumortier et al., Geophysical Research Abstracts, Vol. 15, EGU2013-2083-1, 2013 Jérôme et al., Geophysical Research Abstracts Vol. 15, EGU2013-6989, 2013 [less ▲]

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See detailImpact of grazing on carbon balance of an intensively grazed grassland in Belgium
Jerome, Elisabeth ULg; Beckers, Yves ULg; Beekkerk van Ruth, Jöran ULg et al

Poster (2013, April 09)

This work analyzes the impact of grazing on the carbon balance of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne terrestrial observatory (DTO). The ... [more ▼]

This work analyzes the impact of grazing on the carbon balance of a grassland grazed by the Belgian Blue breed of cattle. The research was run at the Dorinne terrestrial observatory (DTO). The experimental site is a permanent grassland of ca. 4.2 ha located in the Belgian Condroz (50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.). Other studies are conducted at the DTO including measurements of methane (CH4) and nitrous oxide fluxes (Dumortier et al., Geophysical Research Abstracts, Vol. 15, EGU2013-2083-1, 2013; Beekkerk van Ruth et al., Geophysical Research Abstracts, Vol. 15, EGU2013-3211, 2013, respectively). Grassland carbon budget (Net Biome Productivity, NBP) was calculated from Net Ecosystem Exchange (NEE) measured by eddy covariance by taking imports and exports of organic C and losses of carbon as CH4 into account (Soussana et al., 2010). After 2 years of measurements (May 2010 - May 2012), the grassland behaved on average as a CO2 source (NEE = 73 ±31 g C m-2 y-1). After inclusion of all the C inputs and outputs the site was closed to equilibrium (NBP = 23 ±34 g C m-2 y-1). To analyze the impact of grazing on CO2 fluxes, we studied the temporal evolution of gross maximal photosynthetic capacity GPPmax and dark respiration Rd (deduced from the response of daytime fluxes to radiation over 5-day windows). We calculated GPPmax and Rd variation between the end and the beginning of grazing or non-grazing periods (∆GPPmax and ∆Rd, respectively). We observed a significant decrease of GPPmax during grazing periods and measured a ∆GPPmax dependence on the average stocking rate. This allows us to quantify the assimilation reduction due to grass consumption by cattle. On the contrary, no Rd decrease was observed during grazing periods. Moreover, we found that cumulated monthly NEE increased significantly with the average stocking rate. In addition, a confinement experiment was carried out in order to analyze livestock contribution to Total Ecosystem Respiration. Each experiment extended over two days: the first day, cattle was confined in the footprint of the eddy covariance set-up (1.76 ha, 27 LU ha-1) and the second day, it was removed from it. We compared filtered half-hourly data made at 24h intervals, in the presence or absence of cattle, considering that environmental conditions were equivalent (air temperature, wind speed, radiation and wind direction). Results showed that CO2 fluxes were significantly higher when cattle were on the plot. Livestock contribution estimation to CO2 fluxes was on average 6.6 µmol m-2 s-1. [less ▲]

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See detail10. Environnement et gaz à effet de serre
Moureaux, Christine ULg; Aubinet, Marc ULg; Bodson, Bernard ULg

in Bodson, Bernard; Destain, Jean-Pierre (Eds.) Livre Blanc - Céréales (2013, February 27)

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